Field of the Invention
This invention relates to an apparatus for measuring the finish of a surface or the finish of the surface of the interior wall portion of fastener holes.
The standard for surface texture, as determined by the American Standards Association specifies the use of a stylus type instrument for measuring the roughness of surface finishes. Such instruments convert the vertical motions of a stylus as it traverses surface irregularities into electrical signals by means of a transducer. The resulting signals are then conditioned and displayed, usually by a meter, as a surface roughness value. While commerical instruments of this type have been quite successful when applied to relatively flat surfaces, they have heretofore not been well-suited for inspection of the interior wall portions of fastener holes.
Manual positioning of such instruments has resulted in expensive and time consuming procedures to accomplish examination of the desired wall portions of fastener holes while at the same time avoiding the upper and lower edges of such holes. The fixed stroke length of such instruments usually requires more than one setup procedure to inspect the interior walls of holes bored through thicker surfaces. At the same time, the stroke length generally prohibits the inspection of the walls of holes bored through thinner surfaces. Manual operation of such instruments produces inconsistent stylus pressures resulting in unstable and inaccurate surface roughness measurements.